An existing wireless communications network, such as a Global System for Mobile Communications (GSM), a Universal Mobile Telecommunications System (UMTS), or a Long Term Evolution (LTE) system is mainly specific to human-to-human (H2H) communication, and mainly considers a wireless environment such as an outdoor scenario or a common indoor scenario. Currently, the 3rd Generation Partnership Project (3GPP) standard has already started to consider using a wireless network to support machine-to-machine (M2M) communication, that is, machine type communication (MTC). Because some terminal devices applied to M2M communication are located in uninhabited areas such as a basement, a tunnel, a valley, and a forest, signal coverage in these places is relatively poor. In order that the terminal devices located in these areas can properly communicate with a network device, coverage performance, of a wireless network, for the terminal devices located in these areas needs to be enhanced.
In the prior art, a hybrid automatic repeat request (HARQ) mechanism or an automatic repeat request (ARQ) mechanism may be used for a wireless network with short-duration coverage or relatively poor coverage performance. Specifically, when data is transmitted for the first time, if a receiving end (for example, a base station) does not correctly receive the data, the receiving end notifies, by using a negative acknowledgement (NACK), a sending end (for example, a terminal) of a message that the data is not correctly received, and the sending end resends (data retransmission) the data that is not correctly received. The receiving end performs soft combination on the retransmitted data and the previously sent data to improve a probability of correctly receiving the data, so as to enhance coverage performance of the network to some extent.
However, in the prior art, an automatic retransmission mechanism used for coverage enhancement is a transmission mechanism based on a Media Access Control (MAC) layer and/or a transmission mechanism based on a Radio Link Control (RLC) layer. The sending end needs an acknowledgement (ACK)/NACK feedback response mechanism of the receiving end to cooperate in performing the automatic retransmission mechanism. For places with relatively weak signal coverage, the receiving end needs to reply with NACK messages for multiple times to trigger multiple retransmissions performed by the sending end, to improve a probability of successful receiving performed by the receiving end. Consequently, air-interface interaction is frequent, and signaling overheads are large. In addition, the sending end cannot effectively adjust coverage enhancement in a timely manner according to a change of a coverage environment in which the sending end is located, and execution efficiency of coverage enhancement is low.